This application proposes a mixed method, ethno-epidemiological study of drug and sexual risk among young male sex workers Hanoi and Ho Chi Minh City, Vietnam. There are an estimated 8.3 million individuals with HIV infections in Asia, one fifth the disease burden worldwide. Initially thought to be confined to circumspect populations of male IDUs and female sex workers, it is now clear that men who have sex with men are also at high risk. Of particular concern is that concurrent with the rapid increases in STI and HIV infection among young adult male populations in the region, there has also been an expansion of markets for male sex work and international male sex tourism. Largely from socially and economically disadvantaged social strata, many male sex workers have concurrent female heterosexual partners. This constellation of sexual partnering has the potential to contribute to increased heterosexual and perinatal transmission and development of a generalized epidemic. This may also contribute to diffusion of novel subtypes and multiply resistant forms of HIV-1, reflecting the high background prevalence of these viruses in the countries from which much of the international sex tourism client base originates, potentially adding even greater challenge to attempts to "scale up" ARV therapy. The study will be conducted in and through an existing collaboration between researchers at National Development and Research Institutes, Inc. (NDRI), Hanoi Medical University, and the Wadsworth Viral Genotyping Laboratories of the NY Department of Health, and a new collaboration with the Ho Chi Minh City Provincial AIDS Committee. In Study 1, formative ethnography will be used to describe the settings, venues, and overall social milieu in which male sex work is being situated. In Study 2, we will conduct a Capture-Recapture Survey to estimate the size of the male sex worker population in each city. In Study 3, we will conduct a broad cross-sectional study for the purpose of construction of a comprehensive ethno-epidemiological profile of behavioral HIV risk among male sex workers. Study 4 will assess the negative medical consequences in this population using biological markers to screen for the presence of HIV-1, HBV, HCV and STIs, including the use of DBS methods to assess the presence of novel HIV subtypes and treatment-resistant strains of HIV. In Study 5, we will recruit young men who have recently initiated male sex work for participation in a one year series of ethnographic interviews to describe the unique vulnerabilities associated with the early course of male sex work. Study 6 will use data from the earlier studies to develop epidemiological models to assess the impact of behavioral risk among male sex workers on the diffusion of HIV-1 in Hanoi and Ho Chi Minh City. PUBLIC HEALTH RELEVANCE This study seeks to address an important public health question: what is the impact of male sex work on the growing HIV epidemics in Hanoi and Ho Chi Minh City, Vietnam? HIV rates in Vietnam are rapidly increasing, and yet there are limited data on the role that different populations play in this increase. Existing data are based on the assumption that HIV is found primarily in injection drug users and female sex workers, with only recent attention being paid to men who have sex with men. Beyond these groups, male sex workers, who may engage in sexual exchanges with men from foreign countries with high background HIV seroprevalence rates and other infections (exchanges referred to as international sex tourism), are a high-risk s heterosexual and engage in concurrent heterosexual relationships (including traditional marriage and parenting) and who, due to stigma and shame, avoid clinical care. This high-risk group is therefore a likely bridge to the larger population, and may become infected with novel subtypes of HIV and/or treatment-resistant HIV due to their sexual contact with foreign clients. Through comprehensive behavioral interviews, detailed ethnography, and state-of-the art biological tests (including tests for HIV and HCV subtypes and HIV treatment resistance), we will describe the demographic, social, and economic characteristics of the male sex worker population in Hanoi and Ho Chi Minh City, Vietnam, as well as the unique vulnerabilities associated with the onset and early social course of male sex work. We will also describe the prevalence of negative medical consequences associated with behavioral risk among male sex workers in these cities, including infections such as Syphilis, Gonorrhea, Chlamydia, Hepatitis B, Hepatitis C, and HIV-1 (including the prevalence of HIV and HCV subtype heterogeneity and treatment-resistant HIV). In order to explain the impact of these behavioral risks on the spread of HIV in urban centers in Vietnam, we will use sophisticated mathematical techniques (known as epidemiological modeling) and we will report these data in both academic journals and through local community dissemination meetings held in both Hanoi and Ho Chi Minh City.